First, was your daughter pot trained early? Children take two steps forward and one back. My daughter was and at (3)years old she did the same thing. Your teacher said she has accidents during activities, right? So she's doing the same thing at school, but by a different name "accidents". When she's doing it at home is she in the middle of something that she doesn't want to stop? My daughter did not want to stop whatever she was doing to go and pee. When I realized that I was able to handle the situation better. You're trying to "guilt" her into not peeing on the floor, because it makes you sad. That doesn't work for a kid, they need consiquences for their actions.
If your daughter can take her panty off to pee on the floor and put them back on after she's done she is fully potty trained. If she pees at school have the teacher call you and go pick her up. My daughter was surprised to see me in school changing her clothes and stopped peeing at school immediately. I didn't even get to take her home. I told her if she peed on herself again we're going home to discuss it. She never had an accident in school again. For home your saddness or happiness is not in the equation. When it comes to potty training or retraining keep your feelings to yourself unless the kid does what you want than positive praise is necessary, because you don't want a power struggle. If she pees on the floor with panty or not she goes into time out for three minutes (she's three) with pee clothes still on and than as you clean her off you explain that peeing is for potty and if she pees on the floor she will be punished with time out each and every time until she stops.